==System Environment==      
-----------------------------------------------------
Regression:  not sure
Non-working platforms: BDW

==Kernel==
--------------------------------------------------
commit ccb80acf8645c77a7542446d7223b3fef996213d
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Fri Apr 10 08:58:01 2015 +0200

drm-intel-nightly: 2015y-04m-10d-06h-57m-17s UTC integration manifest


==Bug detailed description==
-----------------------------
Dpy_3p_media causes WARNING: CPU: 0 PID: 0 at drivers/gpu/drm/i915/intel_uncore.c:558 hsw_unclaimed_reg_debug.isra.8+0x62/0x78 [i915]() on bdw.
It also causes WARNING on drm-intel-testing-2015-03-27 and drm-intel-testing-2015-03-13.
It causes “[drm:hsw_unclaimed_reg_detect.isra.9 [i915]] *ERROR* Unclaimed register detected. Please use the i915.mmio_debug=1 to debug this problem” on drm-intel-testing-2015-02-27 and drm-intel-testing-2015-01-30.
Please see the dmesg 04-10 and 02-27 info.

Output:
<4>[  326.955609] ------------[ cut here ]------------
<4>[  326.955634] WARNING: CPU: 0 PID: 0 at drivers/gpu/drm/i915/intel_uncore.c:558 hsw_unclaimed_reg_debug.isra.8+0x62/0x78  
[i915]()
<4>[  326.955635] Unclaimed register detected before reading register 0x44200
<4>[  326.955637] Modules linked in: dm_mod iTCO_wdt iTCO_vendor_support ppdev snd_hda_codec_hdmi pcspkr i2c_i801  
snd_hda_intel snd_hda_controller snd_hda_codec snd_hda_core lpc_ich mfd_core snd_hwdep snd_pcm snd_timer snd soundcore  
battery parport_pc parport ac acpi_cpufreq i915 button video drm_kms_helper drm
<4>[  326.955655] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.0.0-rc7_drm-intel-testing-2015-04-10+ #1074
<4>[  326.955656]  0000000000000000 0000000000000009 ffffffff817958c7 ffff88014ec03dc8
<4>[  326.955659]  ffffffff8103bd5a 00000000004e0008 ffffffffa00becd6 ffffffff819a3970
<4>[  326.955661]  ffff880002f50068 0000000000044200 ffff880002f50070 ffff880002f50068
<4>[  326.955663] Call Trace:
<4>[  326.955664]  <IRQ>  [<ffffffff817958c7>] ? dump_stack+0x40/0x50
<4>[  326.955673]  [<ffffffff8103bd5a>] ? warn_slowpath_common+0x98/0xb0
<4>[  326.955685]  [<ffffffffa00becd6>] ? hsw_unclaimed_reg_debug.isra.8+0x62/0x78 [i915]
<4>[  326.955688]  [<ffffffff8103bdb7>] ? warn_slowpath_fmt+0x45/0x4a
<4>[  326.955692]  [<ffffffff8105caac>] ? select_task_rq_fair+0x231/0x59d
<4>[  326.955703]  [<ffffffffa00becd6>] ? hsw_unclaimed_reg_debug.isra.8+0x62/0x78 [i915]
<4>[  326.955714]  [<ffffffffa00bee97>] ? gen6_read32+0x49/0x163 [i915]
<4>[  326.955727]  [<ffffffffa00ad0e1>] ? gen8_irq_handler+0x4b/0x345 [i915]
<4>[  326.955730]  [<ffffffff81071db0>] ? handle_irq_event_percpu+0x34/0x15b
<4>[  326.955733]  [<ffffffff81081fb9>] ? update_wall_time+0x524/0x53d
<4>[  326.955735]  [<ffffffff81071f05>] ? handle_irq_event+0x2e/0x4d
<4>[  326.955737]  [<ffffffff81074450>] ? handle_edge_irq+0xba/0xcf
<4>[  326.955740]  [<ffffffff810042fd>] ? handle_irq+0x15/0x20
<4>[  326.955742]  [<ffffffff81003dc0>] ? do_IRQ+0x41/0xc0
<4>[  326.955744]  [<ffffffff8179bc2a>] ? common_interrupt+0x6a/0x6a
<4>[  326.955746]  <EOI>  [<ffffffff8100a00f>] ? default_idle+0x1d/0x8a
<4>[  326.955751]  [<ffffffff8106547f>] ? cpu_startup_entry+0x2c3/0x350
<4>[  326.955754]  [<ffffffff81c82e35>] ? start_kernel+0x415/0x420
<4>[  326.955757]  [<ffffffff81c8282a>] ? set_init_arg+0x4e/0x4e
<4>[  326.955758] ---[ end trace 9f6f9f66a9184c4c ]---

Reproduce steps:
----------------------------
1, xinit&
2, mplayer -vo xv xxxxx